TAKAGI, Kimberly K.; REIHANIFAM, Nadia; FREITAS, Brad; WRIGHT, William G.; Chapman University; Chapman University; Chapman University; Chapman University: Chemical versus cognitive defenses in opisthobranch mollusks.

Across evolutionary time, animals have evolved a variety of predator defenses. We are studying two such defenses in the California sea hare, Aplysia californica. First, Aplysia increases the vigor of its defensive reflexes after a traumatic experience. Such �sensitization� protects the animal’s vulnerable extremities from attack, thereby serving as a cognitive defense. A second adaptation is chemical: sea hares sequester unpalatable secondary metabolites in vulnerable tissues to discourage predation. In this study, we hypothesized an evolutionary trade-off between chemical and cognitive defenses. Previous research reports much less sensitization in Phyllaplysia taylori and almost no sensitization in Dolabrifera dolabrifera relative to Aplysia. If there is an evolutionary trade-off between cognitive and chemical defenses, we would predict that these reductions in cognitive defense should be associated with increases in chemical defenses. Using the hermit crab scavenger, Pagurus samuelis, we tested our prediction. The hermit crabs were starved for 1 week and offered homogenized pellets of Aplysia, Phyllaplysia and Dolabrifera in no-choice experiments. The amount eaten was quantified by measuring pellet weight before and after 30 min feeding trials. Surprisingly both Phyllaplysia and Dolabrifera were significantly more palatable than Aplysia. These results exclude our trade-off hypothesis. We are presently investigating alternative hypotheses that involve a positive relationship between chemical and cognitive defenses. Perhaps for example, both kinds of defenses are together traded off against one or more indirect anti-predator strategies such as larval and adult habitat choice, time of foraging, and camouflage.